Phased array (hereafter PA) ultrasonic instruments have been used in non-destructive testing and instrument (NDT/NDI) applications to perform ultrasonic tests that include weld inspection, bond testing, thickness profiling, in-service crack detection, etc. Phased array probes typically comprise a transducer assembly with from 16 to as many as 256 small individual piezoelectric elements that can each be pulsed separately. Pulse rate, commonly known as pulse repetition frequency, is the rate at which an electrical pulse is applied to a piezoelectric element producing an ultrasound through a testing material. A pulser circuitry is usually employed to perform the pulsing tasks to energize each PA probe's element. A typical pulser circuitry of a phased array inspection system is shown in FIG. 1.
As can be seen in FIG. 1, the typical pulser circuitry mainly comprises two groups of components. The first group comprises a transducer or probe 20, the other portion embodies the whole pulser 10, which further includes electronics such as resistors 12, mosfet 14, diodes 16, analog switches 18, etc.
Ideally, in order to detect flaws with high resolution and high scanning efficiency, a phased array inspection system is setup with a pulse rate as high as possible. One prominent factor limiting the level of pulse rate is the maximum power consumption of the pulser circuit.
The amount of power that is transferred from the ultrasonic pulser circuit to a transducer is affected by the respective electronic components that comprise the pulser itself and by the impedance of the transducer. The transducer impedance magnitude, on the other hand, is affected by the excitation frequency (pulse width) of the pulser and the specific transducer coupled with the PA system and could change during the life of the specific transducer. The ‘real’ transducer impedance, or herein called “adaptive impedance” is therefore probe-specific and operational-setup-specific. Since the adaptive impedance of a transducer is not always readily known, in existing practice, assumed or fixed (static) transducer impedance is often arbitrarily given according to a worst case scenario to limit the maximum pulse rate specification of an instrument.
This limitation of the maximum pulse rate based on the assumed or static transducer impedance often means the phased array system is not set up in a way to provide the optimized pulsed rate. In typical industrial NDT applications where high pulse rate and high voltage is required, the maximum pulse rate specification could be increased up to 100% if the adaptive impedance of the transducer is known. However, existing practice has often seen to use 50 Ohms as fixed worst case transducer impedance. The problem associated with this existing practice is that it limits the performance and efficiency (scan rate and pulse rate) because typical transducer has greater impedance.
As can be seen that one critical factor leading to more accurately and dynamically gauging and optimizing the pulse rate is the capability to accurately measure the real, adaptive transducer impedance according to the probe and PA system setup. More specifically, with the adaptive transducer impedance more closely estimated, the amount of power that is transferred to the transducer versus the amount of power that remain within the pulser at any pulsing cycle is known and the pulse rate can be more accurately established.
Existing efforts addressing the measurement of transducer impedance has been seen in some industrial publications. One is presented by “Measurement of Complex Impedance of Ultrasonic Transducers”, by L. Svilainis and V. Dumbrava. (later as “Svilainis and Dumbrava”). Svilainis and Dumbrava explains a way to measure the complex impedance of ultrasonic transducers with an approach to null out the reactive impedance (imaginary part of the complex impedance) to improve the performance of the transducer. However, for the case of solving the problem herein addressed, which is to maximize the phased array pulse rate, measuring the complex impedance is not of the concern of the present disclosure. What needs to be accurately measured is the resistance (magnitude) impedance, which is the real component of the complex impedance dealt by Svilainis and Dumbrava.
Another publication also by Svilainis and Dumbrava titled “Evaluation of the Ultrasonic Transducer Electrical Matching Performance” is published under ISSN 1392-2114 ULTRAGARSAS (ULTRASOUND), Vol. 62, No. 4, 2007 (later as Svilainis and Dumbrava II). The publication discusses how the performance of the transducer could be improved by adjusting the impedance of the generator. However, the solution taught in this publication does not apply to our pulsing technology, which is unipolar pulser. It applies to pulser using sine wave generator for Svilainis and Dumbrava II.
In addition, Svilainis and Dumbrava II do not deal with or include transducer impedance in their solution.
Another aspect of the background of the present disclosure is the usage of a widely known SPICE electronics simulation tool. A particular usage of the tool for ultrasonic device is mentioned in “SPICE SIMULATION OF TRANSIENT RESPONSES OF TRANSDUCERS AND SPIKE GENERATORS INCLUDED IN E/R ULTRASONIC SYSTEMS”, published online on Digital CSIC by Ruiz Toledo A.; Ramos A.; San Emeterio, J. L.; Sanz Sanchez P. T., which is herein collectively referred as “SPICE”. However, there is no effort seen in using SPICE to seek optimum pulse rate with given energy limit for phased array probes.
Thus, given that the existing practice uses less-than-optimum pulse rate and the existing efforts that do not address the issue effectively, solution providing optimized pulse rate is needed to improve the inspection efficiency.